1. Field of the Invention
The present invention relates to a method for manufacturing a pre-molding leadframe strip, and more particularly, to a method for manufacturing a pre-molding leadframe strip with compact components. The disclosure of the present invention can be applied to a surface-mountable electronic component, such as, but not limited to, light-emitting diodes.
2. Description of the Prior Art
As well known to those skilled in the art, a light-emitting diode composed of a compound semiconductor, such as GaAs, AlGaAs, GaN, InGaN or AlGaInP, as a light-emitting source, is a semiconductor device capable of emitting light of various colors.
With great advances in semiconductor techniques, light-emitting diode devices have been produced to have high luminance and quality characteristics. In addition, fabrication of blue and white diodes has been practically realized, whereby the light-emitting diodes are widely applicable to displays, next-generation lighting sources and the like. Besides, a surface mountable light-emitting diode device is available.
In order to expand the areas of use and in order to reduce production costs, attempts are being made to produce electronic components of ever smaller structural sizes and to arrange more components in a certain area. By way of example, the backlighting of the keys of mobile telephones requires very small light-emitting diodes.
A further compactness of the devices is desirable, but is extremely difficult using conventionally available processes. FIGS. 1a through 1c are top views illustrating a manufacturing process of a conventional pre-molding leadframe strip. As shown in FIG. 1a, a leadframe strip 10 with an array of component regions 22a is formed for supporting light-emitting diode chips by punching out the leadframe strip 10 from a metal sheet or a foil. Each component region 22a includes two metal parts 24a and 26a for mounting a light-emitting diode chip thereon, and comprises a wire-bonded portion and an external electrical connection as well as two empty spaces 28a. 
The leadframe strip 10 is then plated with a metal layer 20 having high conductivity and die bonding adhesion, as shown in FIG. 1b. 
An array of pre-molded structures 42a are formed to surround portions of the leadframe strip 10 with the exception of only electrode portions to be used as the external lead electrodes by means of a pre-molding process, as shown in FIG. 1c. The conventional pre-molding process is a single step cold runner process and implemented with a sprue 30 and multiple forked runners 32. Each of the pre-molded structures 42a formed by the pre-molding process is in the form of polyhedron having an inner cavity to easily mount a desirable target therein, in which a surface facing the component region 22a is opened. FIG. 2 shows the detailed pre-molded structure 42a and the resulted component region 22a. The finished component region 22a includes a function area 48a composed of the chip-attached portion 47a and the wire-bonded portion 49a, the pre-molded structures 42a, the empty spaces 28a and two exposed external electrode portions 44a and 46a. The external electrode portions 44a and 46a of the component region 22a will then be folded to make mountable electrode structures during subsequent packaging processes.
However, such a conventional pre-molding process is disadvantageous in terms of lower throughput as well as leadframe and molding material waste, resulting from loose arrangement of effective component regions caused by space required by forked runners in a single injection molding process. As can be seen in FIGS. 1a through 1c, the conventional pre-molded process is low in mass production efficiency, since a density of the component regions is limited by the single pre-molding process. Moreover, use of such a single pre-molding process means the actual area occupied by the components is very low, thus significantly lowering utilization of precious materials.